Films by anodic oxidation of mercaptoanilines AT Cu electrodes

The anodic oxidation of mercaptoanilines at different metal anodes proves that coherent coatings may be formed in situ on copper only, using the meta isomer. These coatings probably from through the oxidation of an intermediate Cu-3-mercaptoaniline complex, which leaves high copper content in the polymer deposit: however, such materials impart outstanding corrosion protection to the substrate. It is suggested that, after easy dimerization of the monometer to disulfide, C—S coupling reactions play a basic role in the constitution of the polymeric network.     

A kinetic study of methane hydrate formation

The kinetics of methane hydrate formation, after commencement of nucleation, were studied using a semibatch stirred tank reactor. The temperatures studied in the experiments were from 274 to 284 K over a pressure range of 3–10 MPa. The results of the experiments revealed that the formation kinetics were dependent on the interfacial area, pressure, temperature and degree of supercooling. The history of water sample affected the induction delay times for nuclei formation, but it had no observable effects on the overall kinetics of hydrate formation after the nucleation had commenced. A consistent semi-empirical model was formulated to correlate the experimental kinetic data.     

Measurement and differential kinetic analysis of wall temperatures in monolith converters—I kinetic analysis

It is possible to measure axial wall temperature profiles in adiabatic monolith converters under actual reaction conditions. By applying a differential method of kinetic analysis, axial profiles of concentrations at the wall as well as of reaction rates can be derived with proper computation methods. The data thus obtained may serve for further kinetic evaluation, that is for model building and parameter estimation by proven and well-known methods. The whole procedure looks also promising for performing activity tests on fresh and partly deactivated monolith converters. The slightly greater effort of measuring wall temperatures compared with the usual method only to record inlet and outlet temperatures and integral conversions might more than pay off. In the present first part of the paper the differential method of kinetic analysis is developed and tested by some simulation studies. The second part will deal with actual experiments.     

Coalescence behaviour of gas bubbles in aqueous solutions of n-alcohols and fatty acids

Coalescence frequency and coalescence times of bubble pairs formed on two adjacent capillary tubes were determined in aqueous solutions of n-alcoho and fatty acids. The results show, that coalescence times of bubbles are proportional to the surface excess concentration of the solute. Coalescence ti increase with the polarity of the hydrophilic group of the solute, its chain length and the bubble size. Coalescence frequency decrease drastically fro 100% to 0% at a distinct solute concentration. The transition in coalescence behaviour occurs, if the coalescence times becomes greater than the availa contact times of the bubbles. The transition concentration therefore decreases with increasing rate of bubble formation.     

Chemical absorption into concentrated slurry: Absorptions of carbon dioxide and sulfur dioxide into aqueous concentrated slurries of calcium hydroxide

The absorption of sulfur dioxide and carbon dioxide into aqueous calcium hydroxide slurries were performed using a stirred tank with a plane gas-liquid interface at 308 K. The absorption rates were found to be lower than those predicted by assuming that the solid particles are uniformly suspending in the liquid-film as well as the bulk liquid phase.It might be due to the possibility that there is no particle suspending in the vicinity of the interface. The process of gas absorption with reaction in the slurry was formulated by film-theory model incorporating the presence of an inert region in which there is no particle. The observed absorption rates of sulfur dioxide and carbon dioxide were successfully predicted by the proposed model.     

A unified approach to transport phenomena in polymeric media—I Diffusion in polymeric solutions,gels and melts

An altered free volume state model has been proposed to interpret transport phenomena in diverse media within a unified framework. Its specific application to the interpretation and correlation of data on diffusion in polymer solutions, protein solutions, polymeric gels and blends of polymeric melts has been elaborated. Extensive experimental data from the literature have been analysed within the framework of the model, which confirm its utility. Apart from providing quantitative predictions of the effect of polymer concentration or phase fraction and temperature, the model provides a semiquantitative assessment of the influence of diffusant size and shape, molecular weight of the polymer etc. on diffusional characteristics in the above media.     

An experimental study of oxidation of zinc sulphide pellets

Oxidation of zinc sulphide pellets is carried out in the ranges of 600-826°C temperature, 0.3-0.5 porosity and 15-50 minutes of reaction time. An experimental technique is employed to simultaneously determine the rate of weight loss of the solid and conversions of the solid reactant at various levels in the pellet for different reaction times. A structural model is used to explain the experimental results. It is found that the model predicts both the experimental results obtained under various conditions reasonably well.     

Interferometric study of concentration profiles in solutions near membrane surfaces

A new technique for the observation and interpretation of concentration profiles in diffusion layers at membrane-solution interfaces was developed. The concentration profiles in dilute (0·01N) KCl solutions near an ion-exchange membrane were observed in a modified O'Brien-type wedge laser interferometer while electric current (1·15 and 2·3 mA cm^?2) passed through the solution (25°C). After current reversal, following prepolarization periods of 5–60 s, a concentration minimum develops. The image of this minimum in relation to the membrane surface is not subject to optical deflection and can therefore be accurately determined. From its trajectory, the salt concentration at the membrane surface at the time of current reversal was determined. It was found that as this concentration dropped to the order of 10^?3–10^?4M (“critical concentration”) significant deviations occurred between observed trajectories and those computed from a theory based on the Nernst-Planck equations. These deviations are believed to be caused by substantial migration of H⁺ and OH^?. While these measurements indicate the order of magnitude of the critical concentration, additional measurements are necessary for quantitative determination of this concentration under different physicochemical and hydrodynamic conditions.     

The absorption of CO2 by amine-potash solutions

CO₂ has been absorbed in a stirred vessel into aqueous solutions of MEA and DEA containing K₂CO₃, K₂SO₄ and Na₂SO₄ at 25° and 11°C. While electrolytes in general appear to increase the rate of reaction between CO₂ and both MEA and DEA, K₂CO₃ increases the rate of reaction of DEA much more than that of MEA. The addition of K₂CO₃ to solutions of DEA increases the absorption rate, in spite of the decrease in the solubility and diffusivity of CO₂. The observations help to explain why DEA is an effective promoter for the absorption and desorption of CO₂ by hot, concentrated potash solutions.     

A kinetic model for methanol conversion to hydrocarbons

We developed a detailed kinetic model for methanol conversion to hydrocarbons over zeolites. The dimethylether at equilibrium with methanol, generates carbene; it attacks the oxygenates giving light olefins, and the latter forming higher olefins. The olefins, through carbenium ions, form aromatics and paraffins. The kinetic parameters, identified by nonlinear optimization techniques, and the model predictions, agree quite well with the experiment and literature available data.     

Simultaneous absorption of two gases reacting between themselves in a liquid—I exact solutions

Simultaneous absorption and irreversible second order chemical reaction of two gases in an inert liquid have been considered. The nonlinear differential equations describing the absorption process have been solved analytically for particular cases by the use of the Weierstrass elliptic function and Airy functions. It is impossible to obtain a general analytical solution and therefore the accurate numerical solution for the diffusion-reaction process based on the film theory has been developed. The approximate formula for the enhancement factor E_A, in the range of large values of the dimensionless parameter M is given.     

A kinetic study of the reaction between terephthalic acid and ethylene oxide in a nonsolvent system

Kinetics of the reaction between terephathalic acid and ethylene oxide, catalysed by triethylamine, was studied in a high-pressure reactor without using solvent. This reaction was carried out at a temperature range of 80–100°C and at a pressure range of 10–15 Kg/cm² beyond the corresponding vapor pressure of ethylene oxide. Effects of temperature, catalyst concentration, mole ratio of ethylene oxide to terephthalic acid, particle size of terephthalic acid, pK value of the tertiary amine and stirrer speed were experimentally investigated on the yield of bis(2-hydroxyethyl) terephthalate and reaction rates. It was found that the bulk reaction of terephthalic acid with ethylene oxide occurred in the liquid phase. Based on experimental results a reaction mechanism to synthesize bis(2-hydroxyethyl) terephthalate from terephthalic acid and ethylene oxide in a nonsolvent system was proposed, and rate constants were obtained with a model based on this proposed reaction mechanism. The activation energy of the reaction was found to be between 3.67–8.28 kcal/mole in the temperature range of 80–95°C.     

On the mechanism of enzyme-catalysed gas—liquid reactions: Absorption of CO2, into buffer solutions containing carbonic anhydrase

The gas absorption with chemical reaction data of Lee and Tsao [1, 2] (i.e. oxidation of glucose solutions containing glucose oxidase or platinum deposited on activated carbon and absorption of carbondioxide into buffer solutions in the presence of carbonic anhydrase) were reexamined and various reasons for their apparent inconsistency with the classical gas absorption models were suggested.The rate of absorption of carbondioxide into 0.5 gmol/l Na₂CO₃ + 0.5 gmol/l NaHCO₂ in the presence of carbonic anhydrase was measured in a stirred cell and also in a laminar jet and a wetted wall column aparatus. Enhancement in the absorption rate due to enzyme was observed in all three absorbers and the results were found to be compatible with classical mass transfer models (such as Higbie's and Danckwerts' models). On the contrary to Tsao[2], who proposed a two-zone model, which assumes a surface-excess of the enzyme at the gas—liquid interface, these results suggest that the carbonic anhydrase distribution in the liquid is probably uniform.     

A structural optimization approach in process synthesis—I : Utility systems

A mixed-integer linear programming approach is presented for performing structural and parameter optimization in the synthesis of processing systems. This approach is applied to the synthesis of utility systems that have to provide fixed demands of electricity, power for drivers and steam at various pressure levels. A superstructure that has embedded many potential configurations of utility systems is proposed, as well as its corresponding mixed-integer programming model. The application of the model is illustrated with a large example problem.     

The transient response of a CSTR containing porous catalyst pellets: Asymptotic solutions

Transient response of a CSTR containing porous catalyst pellets is analyzed theoretically using a matched asymptotic expansion technique. This singular perturbation technique leads directly to the conditions under which the minima of reservoir concentration occur. The existence of the minima may be used to estimate some inherent parameters of the catalyst pellet.     

Process optimization: A comparative case study

Four recently developed algorithms were tested on a realistic propylene chlorination process simulation. All four are based on successive quadratic programming and interface easily with most sequential modular simulation packages. Using SPAD for simulation, optimal cases were obtained in as few as 29 simulation-time equivalents. The paper includes model details, reactor kinetics, and algorithm performance.     

The effect of homogeneous gas phase oxidations in char particle gasification

Two steady state models have been developed for the simultaneous oxidation and gasification of a single coal char particle. Because of the uncertainty in the relative importance of solid phase and gas phase reaction kinetics in a gasifier environment, the models assume that the velocities for the gas phase oxidations of hydrogen and carbon monoxide are either zero or infinitely fast. The global rates and steady state multiplicities are discussed as functions of particle size, film thickness, gas composition and ambient temperature. The restriction of infinite hydrogen diffusivity assumed by previous investigators is removed. The two models lead to considerably different predictions about the maximum temperature of char particles in coal gasifiers.